The present invention relates to a resistor used for high-density wiring circuit and a method for manufacturing the same.
Japanese Patent Laid Open Publication No. S59-75607 teaches a conventional resistor.
The conventional resistor and the process of manufacturing are described in the following with reference to the drawings.
FIG. 11 shows plan view of a conventional resistor.
Shown in FIG. 11 are an insulating substrate 1, electrodes 2a, 2b provided on both sides of the upper surface of the substrate 1, a resistor element 3 provided between and over the electrodes 2a, 2b and side-face electrodes 4a, 4b which are provided on the side faces of the substrate 1 keeping electrical connection with the electrodes 2a, 2b, respectively. Numeral 5 denotes a trimmed groove formed as the result of trimming operation performed on the resister element 3.
Now in the following, a method for manufacturing the conventional resistor of above structure is described referring to the drawings.
FIG. 12 is a drawing used to illustrate key processes for manufacturing the conventional resistor.
In the first place, electrodes 14 are formed on the upper surface of an insulating substrate 11 of a sheet form; on the surface of which substrate, longitudinal cut lines 12 and lateral cut lines 13 have been provided for later breaking of the substrate. The electrodes 14 are formed independently in respective regions with respect to the direction of longitudinal cut line 12, while, in terms of lateral direction, the electrodes 14 are formed across the longitudinal cut line 12. And then, resistor elements 17 are provided in the form of a thick film laterally bridging the electrodes 14.
Next process is a trimming with a laser beam. The trimming is conducted while the resistance is being measured. The measurement of resistance and the trimming of a resistor element 17 are conducted for each of the resistor elements disposed in lateral direction. For example, each of the resistor elements on the uppermost line is measured the resistance by having a probe on each of the electrodes, and respective resistor elements are trimmed by means of laser beam irradiated thereon.
If necessary, an insulating protection layer of glass, or the like material, is formed on the surface, and then the insulating substrate is separated along the longitudinal cut line 12 to obtain a plurality of substrate sheets of a band shape. Depending on needs, side-face electrodes are provided in the form of a thick film covering both side faces of the band-shaped substrate sheet, and the surface of electrodes are plated if necessary.
After that, separating along the lateral cut line 13 provides individual chip resistors.
As described in the above, probes are put on the upper-surface electrode layers to provide electric current in a resistance layer in order to read voltage drop, and a certain groove is formed therein with a laser beam, or the like means, so that the reading of voltage drop reaches a level that represents a certain specific resistance of the resistance layer.
In the above described conventional structure and the manufacturing method, however, the resistance measured after the trimming dispersed widely depending on positional variation of the probes contacting to the upper-surface electrode layers. This is remarkable among the conventional resistors of low resistance.
The above problem is described more in detail with the aid of illustrations. FIG. 13 shows model paths of a resistance measuring current corresponding to various probe positions during trimming. FIGS. 13(a), (b) and (c) illustrate the cases with the high resistance resistors, while FIGS. 13(d), (e) and (f) are with the low resistance resistors.
In FIG. 13, numeral 23 represents position of a probe making contact to an upper-surface electrode layer, numeral 24 shows a path of electric current during measurement of resistance.
The current path 24 is least influenced by the variation in the position 23 of the probe on the upper-surface electrode layer, among those resistors whose resistance is high (ref. FIGS. 13(a), (b), (c)); therefore, no problem arises.
Among those resistors whose resistance is low, however, because of the small difference in the areal resistivity between the upper-surface electrode layer and the resistor layer, the electric current does not proceed through the entire portion of the resistor layer. A shift in the position 23 of probe contacting to the upper-surface electrode layer results in a significant variation of the current path 24, as shown in FIGS. 13(d), (e) and (f). Namely, the measured resistance depends on the contact position of probe on the upper-surface electrode. Therefore, despite a precise adjustment of the resistance to a prescribed level attained during the trimming operation, actual resistance after trimming disperse because of positional variation in the contact of probe to the upper-surface electrode.
The present invention addresses the above problem involved in the measuring of a resistance of conventional resistors, and intends to provide a resistor of low resistance, including the method of manufacture, the resistance of which precisely falls within a prescribed range regardless of the variation in the contact position of the probes.
A resistor in accordance with an exemplary embodiment of the present invention comprises a substrate, a pair of upper-surface electrodes, which respectively having notched section, provided on both sides of the upper surface of the substrate, a resistor layer provided so that it is connected electrically to the upper-surface electrode layers, a protective layer formed to cover at least the resistance layer, and a couple of side-face electrodes which are provided on both side faces of the substrate so that the side-face electrodes can be electrically connected to the upper-surface electrode in a state where the side-face electrodes overlap on part of the upper-surface electrodes.
Because of the notched section disposed in the pair of upper-surface electrodes provided on both sides of the upper surface of the substrate, path of the electric current flowing in a resistor element remains in a same stable route even if contact position of the probes varies during the trimming operation. Thus, even among the resistors of low resistance, their resistance can be controlled precisely to be within a prescribed range.